1. Field of the Invention
The present invention generally relates to optical modules and optical recording and/or reproducing apparatuses, and more particularly to an optical module which is usable as a light source for generating light beams, and an optical recording and/or reproducing apparatus which records information on and/or reproduces information from a recording medium using the light beams generated from such an optical module.
An optical module of an optical pickup generates a light beam from a semiconductor laser. The light beam is used to record information on and/or reproduce information from optical recording media which include optical disks such as a compact disk (CD) and high-density optical disks such as a digital versatile disk (DVD).
2. Description of the Related Art
Recently, various kinds of optical recording media, including optical disks and high-density optical disks, have been proposed. The optical disks include the CD, CD-R and CD-RW. On the other hand, the high-density optical disks include the DVD and S-DVD. Ideally, it is desirable for a single optical recording and/or reproducing apparatus to be able to recording information on and/or reproduce information from a plurality of kinds of optical disks.
However, an optical pickup which is used for the recording and/or reproduction of information using the optical disk such as the CD, CD-R and CD-RW generates a light beam having a wavelength of 780 nm. A beam spot of this light beam cannot be converged to the size of a pit formed on the high-density optical disk such as the DVD and S-DVD.
On the other hand, an optical pickup which is used for the recording and/or reproduction of information using the high-density optical disk such as the DVD and S-DVD generates a light beam having a wavelength of 650 nm. But a pigment used in the optical disk such as the CD-R cannot reflect this light beam and thus light beam will be transmitted through the optical disk such as the CD-R, thereby making it impossible to reproduce the information from the optical disk such as the CD-R.
Therefore, in order to record information on and/or reproduce information from the optical disk such as the CD-R and the high-density optical disk such as the DVD using a single optical recording and/or reproducing apparatus, it is necessary to provide two semiconductor lasers in the light source part of the optical pickup to respectively generate the light beams having the wavelengths of 780 nm and 650 nm.
But in order to use a common optical system for the two light beams which have the wavelengths of 780 nm and 650 nm and are generated from the two semiconductor lasers, it is necessary to set the two light emission points close together as much as possible. Accordingly, a semiconductor laser unit has been proposed, in which a semiconductor laser chip for generating the light beam having the wavelength of 650 nm and a semiconductor laser chip for generating the light beam having the wavelength of 780 nm are arranged horizontally on a single package. However, according to this proposed semiconductor laser unit, the location of the light emission points are affected by the width of each semiconductor laser chip and the width of a sub-mounting member, and an interval of the light emission points of the two semiconductor laser chips becomes approximately 300 μm to 400 μm and large. As a result, it becomes extremely difficult to design the optical system of the optical pickup.
Hence, a method of artificially reducing the interval between the two light emission points using reflection surfaces has been proposed in a Japanese Laid-Open Patent Application No. 11-39684, for example. FIG. 1 is a diagram showing an optical module employing this proposed method, and corresponds to FIG. 2 of the Japanese Laid-Open Patent Application No. 11-39684. In FIG. 1, a part surrounded by a dotted line is shown on an enlarged scale on the right portion of this figure. A detailed description of FIG. 1 will be omitted in this specification, because it is described in the Japanese Laid-Open Patent Application No. 11-39684.
As shown in FIG. 1, a sub-mounting member 32A has a triangular cross section with reflection surfaces 32B and 32C. A laser beam B1 output from a semiconductor laser 34 is reflected by the reflection surface 32B, and a laser beam B2 output from a semiconductor laser 36 is reflected by the reflection surface 32C. Because the laser beams B1 and B2 are reflected and bent by the reflection surfaces 32B and 32C, it is possible to artificially reduce the interval between the two light emission points. In FIG. 1, a reference numeral 30 denotes a support plate, a reference numeral 32 denotes a support body, and a reference numeral 38 denotes a cap.
In order to realize the method proposed in the Japanese Laid-Open Patent Application No. 11-39684, it is necessary to provide the sub-mounting member 32A having the triangular cross section. However, it is difficult to accurately form the sloping surfaces of the sub-mounting member 32A having the triangular cross section, particularly when the inclination angle of the sloping surfaces is 45 degrees. Because the sloping surfaces determine the reflection surfaces 32B and 32C, inaccurate sloping surfaces cause inaccurate reflections at the reflection surfaces 32B and 32C.
Although several techniques have been proposed to make a member having a triangular cross section with sloping surfaces having an inclination of 45 degrees, none are actually capable of stably mass-producing the member with a high accuracy. Alternatively, it is conceivable to use microprisms to realize a member having the triangular cross section, but it would be extremely difficult to accurately mount the microprisms. Furthermore, since the use of the microprisms will make the member expensive, the use of such a member in the optical pickup will make the optical pickup too expensive from the practical point of view.
Accordingly, the proposed method of artificially reducing the interval between the two light emission points using the reflection surfaces require parts which are both expensive and unsuited for mass-production.